The invention relates to a method of manufacturing a passive fiber optic component. The component comprises at least two optical fibers, each having a core of core glass, a cladding of cladding glass with a refractive index lower than that of the core glass, and an outer coating. In the method, a part of each fiber is bared by removal of the outer coating over a given length from one end of the fiber. The bare parts of the fibers are subjected to an etching treatment whereby a portion of the etched part of each fiber is given a conical shape. The etched portions of the fibers are then arranged against each other in a tube of a glass having a refractive index lower than that of the core glass of the fibers. By applying heat, the tube is fused to the fibers and the bare parts of the fibers are fused together. Finally, the fused fiber bundle is provided with a polished end face.
A method for manufacturing a fiber optic component is described, for example, in U.S. Pat. No. 4,291,940 and in European Patent Application No. 0,123,396. These publications describe the manufacture of couplers according to a hot processing method, the so-called fused biconical taper technique. In this method two fibers are twisted and are then heated and stretched in such a manner that a coupler with a symmetrical biconical configuration is obtained.
In the biconical taper method, the risk of damage of the fiber and of deformation of the fiber core is comparatively high. The method is only suitable for the manufacture of certain types of components, is not readily reproducible, and is not suitable for use in mass production. Furthermore the input fiber can be recognized on the output side, which means that there is no uniform distribution of the input power.
The first method discussed above is described in British Patent Application No. 1,427,539 (corresponding to U.S. Pat. No. 3,933,455). In this method the fibers are not twisted. The fibers are drawn down together with the glass tube in which they are inserted to provide a tapered zone from which interstices between the fibers have been eliminated. The presence of a taper in this zone means that the diameter of the end face has to be selected by arranging it at an appropriate distance along the length of the tapered zone. Considering the core diameter of the fibers to be treated, (50 .mu.m or smaller), it will be difficult to select the correct diameter of the end face within close tolerances. The taper angle is dependent on several parameters and may vary from fiber bundle to fiber bundle.